The present invention relates to a liquid supplying apparatus that includes a liquid storage device storing liquid and a supplying device pressurizingly supplying the liquid to the liquid storage device, and supplies the liquid stored in the liquid storage device to an ejection device, and relates to a liquid ejecting apparatus provided with the liquid supplying apparatus.
In a typical conventional recording head of an inkjet recording apparatus, a sub-tank is installed to temporarily store ink to be supplied to the recording head. When an ink cartridge is replaced for replenishment of ink into the sub-tank, air is likely to enter into and be accumulated inside the sub-tank. When ink is supplied to the sub-tank using an ink supply tube made of a material having air-permeability, air which enters through the wall of the ink supply tube little by little over a long time period will be accumulated inside the sub-tank.
During formation of an image, such air accumulated inside the sub-tank is mixed into ink to be ejected from the recording head. This sometimes causes an ink ejection failure, resulting in a lower quality of a formed image.
There is a known technology to discharge air which has entered into the sub-tank. According to the technology, an atmosphere communication hole is provided in an upper portion of the sub-tank, and the atmosphere communication hole is provided with a gas-permeable membrane, which is permeable to gas but impermeable to liquid, in order to separate the inside of the sub-tank and the atmosphere. In this case, ink is pressurizingly supplied into the inside of the sub-tank periodically, and only air accumulated inside the sub-tank is discharged.
However, there is a problem that backflow of air into the inside of the sub-tank cannot be prevented by only using the gas-permeable membrane. According to the above described technology, air is discharged to the outside of the sub-tank through the gas-permeable membrane when ink is pressurizingly supplied into the sub-tank. At the time of image information, however, a negative pressure is caused inside the sub-tank as the ink is decreased, so that air flows back into the inside of the sub-tank through the gas-permeable membrane. Accordingly, it is required to provide a check valve, besides the gas-permeable membrane, for preventing backflow of air when a negative pressure is caused inside the sub-tank, such as at the time of image formation.